Various types of injection devices are available for assisting with the injection of a medicament into a patient (human or animal), and which are configured to receive a standard, pre-filled glass or plastic syringe tipped with an injection needle. These devices may have a dose setting mechanism and a main drive spring for driving a plunger into the syringe so as to expel the medicament out through the needle. Injection devices may comprise a further spring for driving the needle out of the device housing into the patient's skin, prior to activation of the main drive spring to expel the medicament.
In order to maintain sterility prior to use, and to avoid “sticking” injuries, the pre-filled syringe is supplied to the injection device assembler with a rubber or plastic sheath or “boot” covering the needle. The boot has an interior space for containing the needle, and a sealing end that abuts the adjacent end of the syringe body to seal that inner space. Immediately prior to use, a user (e.g. healthcare professional or patient) must remove the boot to uncover the needle. This is typically achieved using a boot removal tool that is inserted by a user into the injecting end of the device. The tool comprises a set of sprung fingers that ride over and along the boot as the tool is pushed into the device. The fingers then snap into the junction between the syringe end and the boot. The user can the pull out the tool, bringing the cap with it.
Particularly in the case of expensive medicaments, it is extremely important to minimise the failure rate of assembled injection devices. Considering the boot removal solution outlined in the previous paragraph, it may be difficult to achieve exactly the right degree of flexibility in the fingers to ensure that they can ride over the boot whilst still providing sufficient force to close over the junction at the rear of the boot.
WO 2007/036676 (Cilag GmbH International) discloses an auto injection device comprising a housing and a threaded, removable, protective cap at the injection end of the device. In place, the cap envelopes and closes off the device housing, as well as preventing a delivery locking mechanism on the device from being released. The cap engages with the boot such that removal of the cap also serves to remove the boot, thereby exposing the needle, whilst at the same time releasing the device's locking mechanism. The device is assembled by positioning the cap at the injection end of the device housing and then inserting the syringe and boot into the device. The cap is of greater diameter than the device housing in order to enable it to enclose the injection end of the device.
WO 2007/047200 (Eli Lilly & Co.) provides an injection device comprising a housing and an outwardly-flared needle cap. The needle cap engages with a needle shield or boot on the syringe needle, gripping the boot and allowing it to be removed. The cap is provided with a flat base, allowing the assembled device to be stood upright on a workbench, for instance. To assist this, the cap is flared outwards from the plane of the device housing to provide greater stability.
Further injection devices comprising a housing and boot remover are disclosed in WO 2007/132353 (Becton Dickinson France) and GB 2 437 922 (Owen Mumford Ltd). These boot removers also have an outward-flaring base or collar.